We recently asked executives at a couple of major digital ad agencies what they and their clients think of Facebook.

There was disagreement among the executives within the agencies, with some positive and others negative.

The consensus, however, was negative, especially relative to the prevailing sentiment of a few months ago (which was that Facebook was going to kill Google).

The ad executives generally agreed with my macro concern about Facebook as an advertising space, which is that it's like advertising at a party. Facebook's targeting allows you to precisely target which parties you're going to advertise at, but that doesn't mean the people at the parties are interested in hearing your message.

Contrast that with Google, which shows its ads only after people declare that they are looking for a specific product. In other words, they announce in advance that they're interested in the product and that they are looking for information about it, possibly with the intention of buying it. That's the best advertising context in the history of the world.

The context for Google's ads is vastly more valuable than the context for Facebook's ads. And that's part of the reason why Google is doing $40 billion of revenue and Facebook's only doing $4 billion. Other reasons are that Facebook's younger, Facebook doesn't do "self-serve" as well as Google, and, according to the ad execs we spoke to, Facebook is much harder to work with than Google.

Here's some of what the ad execs said:

Facebook is "totally overhyped"

The ad products are too complicated... hard to figure out and use. Even the terms Facebook uses to describe them change all the time.

Facebook has amazing data about its users, but they won't give us access to it. They won't let us target based on it. That's really frustrating.

It's hard to work with Facebook's ad sales team and Facebook's ad products, especially compared to Google. Google has automated everything. They have great reps and full analytics. It's super-easy to work with them.

It's so frustrating to work with Facebook that it's easier to work with one of their "API" partners (outside firms that manage the campaign). It's easier to hire someone else to do your Facebook campaign.

Facebook doesn't break out mobile impressions in its analytics, so we don't know whether it's working

They're no Google. Google is a money-maker. Display advertising is just a bad business.

On the positive side, one of the reasons Facebook has gotten so successful is that Mark Zuckerberg has been obsessively focused on product quality and not cluttering it up with ads. If he stays focused on that, Facebook will be around for a long time.